Cold welding techniques are useful for repairing cast metal parts, since thermal welding and brazing techniques can cause the fused area to become hard and brittle. Prior methods and apparatus used for cold welding cracks in metal parts are disclosed in my U.S. Pat. Nos. 2,998,645; 4,247,973; and 4,599,781, the disclosures of which are incorporated herein by reference.
The basic method and apparatus is disclosed in U.S. Pat. No. 2,998,645, relating to my invention of tapered plugs to fill the gap and simultaneously pre-stress the locks to inhibit them from working out of the metal due to vibration or cyclic expansion. I also disclose therein a repair plug with a groove-weakened head section designed to shear away at set torque, as a preferred embodiment of tapered plug.
In U.S. Pat. No. 4,247,973, I disclose my invention of a jig tool for aligning a drill bit to facilitate drilling the overlapping hole pattern required for the locks, and the method of using the tool. In U.S. Pat. No. 4,599,781, I disclose my invention of an improvement which is advantageous for repairing cracks in thin metal parts, using small-diameter repair plugs with increased threads per inch.
While the above methods, apparatus and tools are useful for repairing cracks in any cast metal wall, they are extensively used to repair cracks in the combustion and water-jacket areas of automotive engines, where high pressure makes soldering an unacceptable mode of repair. Automotive engine cylinder heads and blocks are usually cast aluminum or iron. The inserted locks act as a staple across a crack to prevent it from propagating by further separation of the metal, while the repair plugs seal the gap and pre-stress the locks.
Consequently, the effectiveness of the seal is dependent upon the degree to which the embedded surfaces of repair plugs are effective in maintaining sealing contact with the threaded bores drilled into the casting. Where the crack is in the wall of a vessel used to contain a fluid under pressure, such as the above described cylinder heads and blocks, or steam pipes, hydraulic reservoirs, and similar containers or housings, it would be advantageous to increase the sealing effectiveness of the repair plugs.
I have found that my present invention achieves such increased sealing effect, and describe hereafter the method and apparatus for achieving this enhanced seal.
The manner in which such objects are achieved by the present invention will be apparent upon reading the detailed description which follows, with reference to the drawings for illustration of a particular embodiment. By way of overview, and to assist cursory searchers who do not wish to read the entire disclosure, the following section is provided as a brief summary disclosure of the invention in perfunctory and informal terms. However, persons seeking to understand the full scope of the invention should be aware that such under-standing can only come from careful reading of the claims found at the end of this document.